The size of wireless communication devices is being driven by the marketplace towards smaller and smaller sizes. Consumer and user demand has continued to push a dramatic reduction in the size and weight of communication devices. To accommodate this trend, there is a drive to combine components and functions within the device, wherever possible, in order to reduce the volume of the circuitry. However, internal antenna systems still need to properly operate over multiple frequency bands and with various existing operating modes. For example, network operators providing service on the fourth generation Long Term Evolution (4G LTE) are also providing service on 3G systems, and the device must accommodate both these systems and their operating frequencies. However, the 4G system uses lower operating frequencies than the 3G system, which translates to a larger antenna.
The need for enhanced operability of communication devices along with the drive to smaller device sizes results in conflicting technical requirements for the antenna. Moreover, in order to operate efficiently, internal antennas require a certain amount of mechanical space within the device, which becomes difficult with the shrinking geometry of these devices. In operation, a monopole antenna, such as a classic PIFA (Planar Inverted-F Antenna) will resonate when its length is electrically one-quarter of the wavelength of the frequency being radiated. A standing wave is established as the antenna gains and stores energy from the source driver. The Q of the antenna can be described as the energy stored per cycle of the driving radio frequency (RF) source. Another way of describing the Q of the antenna is to recognize that; on average, the wave front bounces back and forth Q times before it radiates. Yet another way to describe the Q of an antenna is to say that the voltage at the end of the antenna will rise by a factor Q times that of the driving voltage. The voltage along the antenna will follow a cosine distribution; being zero at the grounded end, being the drive level at the driving point, and Q times the drive level at the open end of the antenna. However, smaller devices require placing components closer together within the device, and therefore closer to the antenna elements, and will typically raise the Q of the antenna. Since the bandwidth of the antenna equals 1/Q of the antenna, the net result of antenna loading will be a reduction in bandwidth.
At present, it is desired to create dead air space around the antenna to guarantee its radiating efficiency. However, a problem arises in that any circuits that are near the antenna are subject to radiation from the antenna and will tend to detune the antenna. Additionally, any non-linear semiconducting junctions coupled to the RF field from the antenna can rectify the RF energy and cause unwanted harmonics to be radiated. This condition is exaggerated by closeness of the antenna to the adjacent circuits.
Shielding is the classic approach to de-couple adjacent circuits from the intentional radiators. However, a further problem arises when the shields invade the antenna space. The shields cause field and pattern changes as well as antenna detuning. Of course, the antennas can be readjusted and compensated for the invasion of the circuit shields, but generally at the expense of the bandwidth of the antenna system. At LTE frequencies, this bandwidth problem is severe even before the shield invades the space of the antennas. Therefore, the shields can then make a severe problem even worse.
Accordingly, there is a need to address the issue of electronic components located in close proximity to antenna elements, such that the electronic components do not degrade the antenna performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.